STOP VALVES FOR PISTONS OF SELF-REGULATING HYDRAULIC DEVICES

Abstract: The disclosed valve comprises a passage body (18) having a substantially cylindrical shape and axially coupled to the inner end of the stem (3) of the device (1) and a stop body (19) which has a substantially cylindrical shape and coaxially arranged with respect to said stem (3) and which may slide tight thereon. The passage body (18) has passage orifices (23) through which the liquid fluid (F) contained in the body (2) of the device (1) may circulate. The stop body (19) has a stop seal (29) which may close the orifices (23) of the passage body (18) and a perimetral widening (30) provided with a clamping seal or ring (33) and splines (31) through which may circulate freely said liquid fluid (F). Application to the car industry.

Description: The present invention relates to a cutoff valve for pistons of hydraulic self-adjusting devices, in particular for use in hydraulic self-adjusting devices designed for the permanent, automatic adjustment of the length of control cables. BACKGROUND OF THE INVENTION Hydraulic self-adjusting devices for the permanent,automatic adjustment of the length of control cables are widely known and generally consist of steel cables provided with a protective sheath and attached to an actuating mechanism, such as a pedal for example, with an associated mechanism, such as the clutch of a car for example. These self-adjusting devices carry out adjustment independently of the initial adjustment of the length of the control cable, which is normally carried out when the cable is fitted by means of devices designed for the purpose that operate only during said initial adjustment process. The Spanish patent P 9002014 (equivalent to EP-A-0494276) describes a hydraulic self-adjusting device which consists basically of a cylindrical main body, joined to the mechanism to be actuated, and an adjustment rod, one of the ends of which, the external end, is attached the control cable, whilst the other end, the internal end, has an piston provided with a cutoff valve, said piston defining two semi-chambers inside the main body between which the hydraulic fluid can flow. Furthermore, said device comprises an adjustment spring and volumetric compensation means. This devices operates in such a way that the required increase in length of the control cable as a result of the mechanical demands placed on the mechanism it actuates (for example the progressive wear of the facing on the clutch plate of a car) is provided by the increase in length of the portion of the adjustment rod which protrudes from the main body of the self-adjusting device. One of the cutoff valves for such hydraulic self-adjusting devices which is described by said patent P 9002014 comprises a through element, a cutoff element and an opening spring which works in compression, these elements being arranged coaxially with the adjustment rod. The purpose of the opening spring is to maintain the cutoff valve open so that the liquid fluid can flow between the two semi-chambers of the main body when the adjustment rod is not being pulled by the control cable. The cutoff valve establishes the hydraulic communication between the two semi-chambers by means of the close fit between the cutoff element of the valve and the inner wall of the main body. This cutoff valve described by the Spanish patent P 9002014 suffers from the drawback that it consists of a large number of components, which increases the cost of production of the valve as well as its assembly. In particular, the cutoff element (or shut-off member) is subjected to the permanent opening spring to separate said cutoff element from the through element (or passage member) when the adjustment rod is no longer actuated. This structure arises important difficulties for the liquid being inside of the main body to flow from the area situated at one side of the cutoff element to the area situated at the other side, when the clutch is slightly (and mainly involuntarily) pressed by the driver; in such cases, the spring of the prior art forces the piston to move and for this reason the adjustment of the clutch cable is negatively affected. To overcome this problem, it is necessary to eliminate said spring and to facilitate the flowing of the liquid fluid from one side of the cutoff element to the other side. The patent document GB-A-2008716 concerns a telescopic shock absorber and describes throttle bores whose function is completely different from the means incorporated to the present invention. Said bores are intended to allow the passage of relatively great amounts of liquid fluid to absorb shocks. Instead, the present invention refers to a hydraulic self-adjusting device in which the quantities of liquid fluid flowing along are almost incalculable. DESCRIPTION OF THE INVENTION In order to provide a new type of cutoff valve that provides a solution to the drawback described above, a cutoff valve for pistons of hydraulic self-adjusting devices is disclosed which has a new structure and high operational reliability. The cutoff valve according to the invention constitutes the body of the piston of a hydraulic self-adjusting device such as those described above, i.e. a hydraulic self-adjusting device which comprises the following known elements: a main body which is cylindrical, elongated and hollow and which contains a liquid fluid; an adjustment rod, one of the ends of which, the internal end, is fitted with said piston whilst the other end, the external end, protrudes from the main body by a variable amount and is attached to the corresponding end of the control cable; an adjustment spring arranged inside the main body coaxially with the rod, said spring working constantly in compression, one of its ends resting against the end of the main body from which the rod protrudes, its other end resting against the internal end of the rod by means of a transverse support shoulder joined to said rod, such that the spring tends to constantly push the rod towards the interior of the main body. The cutoff valve according to the invention consists of a through element and a cutoff element. The through element is attached to the internal end of the adjustment rod such that is forms an integral part thereof. The cutoff element is arranged coaxially with the adjustment rod such that it can slide along it over a length determined by the distance between the through element and the transverse support shoulder of the rod. The through element has an essentially cylindrical shape and is provided with a plurality of longitudinal through holes through which the liquid fluid contained within the main body can flow. The through element is also provided with a peripheral groove which is coaxial with the adjustment rod, the size of said groove being such that is fitted with a selaing ring which, by elastic reaction, presses constantly against the inner surface of the wall of the main body, thereby preventing the liquid fluid from passing via the close fit between said wall and said sealing joint. The cutoff element of the valve which forms the object of the present invention is essentially cylindrical in shape and has a central through hole through which the adjustment rod passes with a tight fit, the end of the cutoff element which faces the through element having a coaxial front groove in which is fitted a cutoff joint, the size of said cutoff joint being such that when the valve is in the closed position it blocks the through holes of the through element, preventing the liquid fluid from flowing. The cutoff valve which forms the object of the present invention is characterized in that between the cutoff element and the through element there is no spring, that is, when the cutoff valve is open, the cutoff element is pressed in the opening direction exclusively by the liquid fluid. It is also characterizing that said cutoff element has a peripheral thickening in which are arranged several longitudinal channels through which the liquid fluid contained within the main body can flow freely, said thickening having a coaxial groove that contains a sealing joint or ring which, by elastic reaction, presses constantly against the inner surface of the wall of the main body. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate the cutoff valve for pistons of hydraulic self-adjusting devices which forms the object of the present invention. In said drawings: Figures 1 and 2 are partial section views showing the valve according to the invention fitted in a hydraulic self-adjusting device with the valve in the open and closed positions respectively. Figure 3 is a cross sectional view taken across the line III-III of figure 1. DESCRIPTION OF A PREFERRED EMBODIMENT The cutoff valve VC for pistons of hydraulic self-adjusting devices that forms the object of the present invention, and which is described herein by way of example of a preferred embodiment, is attached to the self-adjusting device 1 shown in figures 1 and 2, said device 1 being designed the carry out the constant, automatic adjustment of the length of a control cable which, for greater clarity, is not shown in the drawings. As has been said, it is understood that said control cable forms part of any mechanism in which its operation requires the constant adjustment of the length of said cable, as for example in the case of the control cable attached to the pedal which operates the clutch of a car. The self-adjusting device 1 shown in the drawings therefore constitutes only an illustrative example and may adopt any other configuration which is suitable for a particular application without affecting the basic concept of the invention. The self-adjusting device 1 comprises a main body 2 which contains the liquid fluid F , an adjustment rod 3, an adjustment spring 4 and a piston 5, said piston 5 defining two semi-chambers 6 and 7, front and rear respectively, inside the main body 2. The diagrams show that the main body 2 has an elongated, hollow, essentially cylindrical shape, at the front end A of which is an axial extension 8 that enables the device 1 to be attached to a fixed point 9, and at the rear end of which is a closing cover 10 that may comprise volumetric compensating means which, for the same reasons as described above, are not shown in the drawings. Figures 1 and 2 show that the front or external end 11 ofthe adjustment rod 3 protrudes from the main body 2 via a through hole 12 such that it can slide with a tight fit, said hole 12 being provided with sealing means 13 to prevent the leakage or escape of the liquid F to the outside. The piston 5 is arranged at the rear or internal end 14 of the rod 3, said piston comprising the cutoff valve VC which forms the object of the present invention. Figures 1 and 2 show that the adjustment spring 4 is helicoidal, has an essentially trunco-conical shape and is arranged coaxially with the adjustment rod. The spring 4 works constantly in compression, its wider diameter resting against a step 15, via a washer 16, which defines the hole 12 in the front end A of the main body, the smaller diameter of the spring 4 resting against the transverse support shoulder 17 fixed to the interior end 14 of the adjustment rod 3. In this way, the elastic reaction of the adjustment spring 4 tends to constantly force the protruding portion of the adjustment rod 3 towards the interior of the main body 2. The above description of the self-adjusting device is known and is commonly used in self-adjusting devices designed to carry out the constant, automatic adjustment of the length of control cables. The diagrams show that the cutoff valve VC that forms the object of the invention comprises a through element 18 and a cutoff element 19, both produced preferably by the injection of a light alloy material such as the zamak alloys. The through element 18 has an essentially cylindrical shape and is formed by injection onto the knurling provided for the purpose on the internal end 14 of the adjustment rod 3. In this way, the knurling 20 is therefore inside the cavity 21 of the through element 18 such that said through element 18 forms an integral part of the adjustment rod 3. With this arrangement, during the operation of the device 1, the through element 18 is prevented from changing its position relative to the adjustment rod 3, i.e. the through element 18 is prevented from rotating about the adjustment rod 3. The cutoff element 19 also has an essentially cylindrical shape and is arranged coaxially with the adjustment rod 3 by means of the axial hole 22, the size of said hole 22 being such that the cutoff element 19 can slide with a tight fit on said rod 3 over the portion that lies between the through element 18 and the transverse support shoulder 17. Figures 1 and 2 show that the through element 18 is provided with through holes 23 through which the liquid fluid F can flow, the rear opening of said holes 23 having a channel 24 designed to increase the passage cross section of the fluid F in said portion of the hole 23. The through element 18 is provided with a peripheral groove 25 in which is fitted a sealing joint 26 which, by elastic reaction, prevents the liquid fluid F from passing via the close fit between said sealing joint 26 and the inner surface 27 of the main body 2. The end of the cutoff element 19 which faces the through element 18 has a front groove 28 which is coaxial with the adjustment rod 3 and which defines a housing in which a sealing joint 29 is firmly fitted. Laterally, the cutoff element has a peripheral thickening 30 provided with three longitudinal channels 31, arranged at regular intervals, through which the liquid fluid F can flow freely. The peripheral thickening 30 has a coaxial groove 32 in which a sealing joint or ring 33 is firmly fitted and which, by elastic reaction, presses constantly against the inner surface 27 of the main body 2. With the self-adjusting device 1 assembled according to the requirements of each specific application, the operation of the cutoff valve VC according to the invention is as follows: In figure 1 the cutoff valve VC is open. In this situation the liquid fluid F can flow freely between the two semi-chambers, front 6 and rear 7, of the main body 2 via the longitudinal channels 31 of the cutoff element 19 and the longitudinal through holes 23 of the through element 18. The cutoff element 19 maintains its position relative to the through element 18 by means of the elastic reaction of its sealing joint or ring 33 which, as has been said, presses constantly against the inner surface 27 of the main body 2. When the adjustment rod 3 is pulled by a force FU which is greater than the elastic reaction of the adjustment spring 4, said rod 3, together with the through element 18 of the cutoff valve VC of the invention which is joined to it, are made to slide towards the outside, the cutoff element 19 remaining in the position it occupied before the force FU was applied due to the action of its sealing joint 33. As the rod 3 and the through element 18 move, the adjustment spring 4 is further compressed and a certain volume ofliquid fluid F flows through the longitudinal channels 31 of the cutoff element 19 and the through holes 23 of through element 18. The through element 18 continues to move until it meets the cutoff element 19, as shown in figure 2, at which point the sealing joint 29 of the cutoff element 19 blocks said holes 23 in the through element 18, preventing the liquid fluid F from passing through them. Thereafter, the incompressibility of the liquid fluid F inside the front semi-chamber 6 of the main body 2 causes the adjustment rod 3 to stop moving inside the main body 2 at the same time that the rod 3, the through element 18 and the cutoff element 19 become joined together. When the force FU applied to the adjustment rod 3 stops acting, the elastic reaction of the adjustment spring 4 forces the rod 3 towards the rear end P of the main body 2, such that the cutoff element 18 joined to it separates from the cutoff element 19. When the through element 18 and cutoff element 19 separate, the sealing joint 29 of the cutoff element 19 no longer blocks the through holes 23 of the through element 18 such that the liquid fluid F can circulate freely through them. It is during the opening of the cutoff valve, i.e. during the separation of the through element 18 and cutoff element 19, that the volumetric compensation dynamics of the liquid fluid F contained in both the front 6 and rear 7 semi-chambers, via the channels 31 of the cutoff element 19 and the through holes 23 of the through element 18, overcoming the elastic reaction of the sealing joint or ring 33 of the cutoff element 19, cause the cutoff element 19 to move towards the front end A of the main body 2. The amount of this displacement of the cutoff element 19 is a function of the variation in the length of the portion of the adjustment rod 3 contained within the main body 2 relative to the length of said portion of the rod 3 before it was pulled by the force FU applied to its front end 11. In this way, the cutoff valve VC that forms the object of the invention is once again arranged to operate as explained above and, as described in the previous paragraph, the cutoff element 19 occupies a new position relative to the through element 18 according to the mechanical demands to which the adjustment rod 3 of the device 1 is subjected. Thus, apart from comprising a reduced number of components, giving it a high operational reliability as well as a reduced production cost, the valve VC which forms the object of the invention provides a solution to the limitations of some known types of cutoff valve due to the relatively reduced volume of liquid fluid F which flows through the valve during the cutoff operation when it is forced by the adjustment rod.

Claims: A cutoff valve for pistons of hydraulic self-adjusting devices (1) consisting essentially of the following known elements: a main body (2) which is cylindrical, elongated and hollow and which contains a liquid fluid ( F ); an adjustment rod (3), one of the ends of which, the internal end (14), is provided with a piston (5) whilst the other end, the external end (15), protrudes from the main body (2) by a variable amount; an adjustment spring (4) arranged inside the main body (2) coaxially with the rod (3) and working constantly in compression, one of its ends resting against the front end ( A ) of the main body (2) from which the rod (3) protrudes, its other end resting against the internal end (14) of the adjustment rod (3) by means of a transverse support shoulder (17) joined to said rod; a cutoff valve ( VC ) which constitutes the piston (5) and which consists of a through element (18) and a cutoff element (19), both of which have an essentially cylindrical shape and wherein: the through element (18) is attached by fixing means to the internal end (14) of the adjustment rod (3) and has a plurality of longitudinal through holes (23), through which the liquid fluid (F) contained within the main body (2) can flow, and a peripheral groove (25) which is coaxial with the adjustment rod (3), the size of said groove being such that is fitted with a sealing joint (26) which, by elastic reaction, presses constantly against the inner surface (27) of the main body (2), preventing the liquid fluid ( F ) from passing via the close fit between said wall (27) and said sealing joint (26); said cutoff element (19) being arranged coaxially with the adjustment rod (3) by means of a central through hole (22), the size of said through hole (22) being such that cutoff element (19) can slide on the adjustment rod (3) with a tight fit over a length determined by the distance between the through element (18) and the transverse support shoulder (17) of the rod (3), the end of said cutoff element (19) which faces the through element (18) having a coaxial front groove (28) in which is fitted a cutoff joint (29), the size of said cutoff joint (29) being such that when the valve ( VC ) is in the closed position it blocks the through holes (23) of the through element (18), preventing the liquid fluid F from flowing; and is characterized in that: when the cutoff valve ( VC ) is open, the cutoff element (19) is pressed in the opening direction exclusively by the liquid fluid ( E ), and in that said cutoff element (19) has a peripheral thickening (30) in which are arranged several longitudinal channels (31) through which the liquid fluid (F) contained within the main body (2) can flow freely, said thickening (30) having a coaxial groove (32) that contains a sealing joint or ring (33) which, by elastic reaction, presses constantly against the inner surface (27) of the main body (2). A cutoff valve according to claim 1, characterized in that the means of fixing the through element (18) to the internal end (14) of the adjustment rod (3) comprise peripheral knurling (20) on said internal end (14), the through element (18) being formed onto said knurling (20) by injection.

Inventors: GABAS CEBOLLERO CARLOS, GABAS CEBOLLERO, CARLOS
Applicants: FICO CABLES SA, FICO CABLES, S.A.
Application year: 1994
Main classification: F16C1
IPC codes: F16D25, F16C1, F16D13